Method and system for varying and regulating a motor speed

ABSTRACT

The invention concerns a method for varying and regulating the speed of a motor powered from a voltage source via a triac, comprising, at least once every alternating voltage interval, the following steps: computing a surface value (S I ) corresponding to the current absorbed (I(M)) in a time window (FT) defined between a current switching-on time (t i ) and a following current switching-off time (t f ); computing an interval of the next triac-blocking time (t′); and controlling the starting of the triac when the blocking time (t′) has elapsed. The invention is useful in particular for household electric and house automation appliances operating at variable speed.

The present invention relates to a process for the variation andregulation of the speed of a motor. It also relates to a system for thepractice of this process. It is more particularly concerned withmonophase AC motors such as universal motors.

Present processes for the regulation of the speed of a motor is either adirect measurement of the speed, or an estimation of the speed fromobservation and measurement of the physical parameters such as adifference of potential proportional to the speed, or the currentintensity drawn by the motor. In this latter case, it is a matter ofmeasuring at the terminals of a shunt placed in series with the motor, adifference of potential proportional to the drawn current. The signal isthen integrated and then compared with a reference voltage. The resultof this comparison leads to a slowing of triggering of the triac whichpermits compensating variations of speed resulting from an overload or aloss of load of the motor. This regulation process is widely used andparticularly in integrated circuits that are specialized or dedicated tospeed regulation.

The object of the present invention is to provide a new process for theregulation of speed which offers a greater flexibility of use than thepresent processes, whilst costing less.

This object is achieved with a process to cause to vary and to regulatethe speed of a motor supplied from an AC source via switch meanscontrolled to apply to this motor a voltage of variable waveform,comprising an adjustment of the periodical instance of triggering saidcontrolled switches.

According to the invention, this process comprises moreover at least onetime per period of the alternating voltage, the following steps:

a surface quantity is calculated corresponding to the current drawn in atime window defined between an instant of establishing the current and afollowing instant of extinguishing this current;

a duration of the next time for blocking the control switch means iscomputed,

and the triggering of said switch means is controlled at the end of thisblocking time.

There is thus obtained with the process according to the invention abetter reliability of taking account of the physical parameter whichconstitutes the current intensity drawn by the motor. This processmoreover offers the possibility of controlling a keyboard, a display, orany other safety function or member. There can thus be provided thepossibility of adjusting the speed by use of a keyboard.

Speeds or sequences of operation can be preprogrammed. The regulationprocess according to the invention can be used for low speeds. There canmoreover be provided a limitation of the maximum load current and thedetection of the condition of the triac (in short circuit or in opencircuit). It is to be noted that the regulation of the speed obtained bythe process according to the invention will be more effective than thatobtained with the present regulation processes.

The computation of the surface quantity is preferably carried out in thefollowing manner:

a plurality of samples are taken of the current intensity drawn by themotor, in a time window comprised between an instant of establishing thecurrent and an instant of extinguishing this current;

the elements of surface are computed from these taken samples; and

the summation of the surface elements is carried out to determine aquantity of surface corresponding to the current drawn by the motorduring a conductive phase of the controlled switch means.

In one preferred embodiment of the process according to the invention,there is calculated a preliminary duration t′ of the next time ofblocking the control switch means by applying the followingrelationship: $t^{\prime} = {\frac{T_{v}}{2} - {k_{v} \cdot P_{I}}}$

in which

T_(v) is the period of alternating supply voltage,

k_(v) is a proportionality factor related to the type of motor and tothe desired speed, and

P_(I) is a parameter associated with calculated quantity of surface.

For operating regimes in which there is no linear relation between theparameters of quantity of surface and blocking time, the parameter P_(I)is then preferably used as a pointer for a memory zone containing valuesof blocking time t′ corresponding to values of the surface quantity.

When this linearity is substantially verified, there is then taken forthe parameter PI the surface quantity S_(I).

For transitional regimes in which the motor requires an energysupplement, the process according to the invention comprises moreoverpreferably a correction of the duration of each next blocking timecorresponding to a difference between the next blocking time t⁺ and thelast applied blocking time t⁻ limited to a predetermined fraction f ofthe difference between the new computed blocking time t′ and the lastapplied blocking time t⁻.

Moreover, a computation of the coefficient of energy correction C iscarried out by applying the relationship:$C = {2\left( {{1\text{,}5} - {\sin \left( {2 \cdot \pi \cdot \frac{t^{+}}{T_{V}}} \right)}} \right)}$

and then the predetermined fraction f is divided by this energycorrection coefficient C.

On the contrary, for transitional regimes corresponding to a decrease ofthe conduction time of the controlled switch means, there can bedirectly applied the new computed blocking time.

The surface quantity S_(i) can be computed by applying the followingrelation:$S_{i} = \left( {\frac{I_{1} + I_{n}}{2} + {\sum\limits_{j = 2}^{j = {({n - 1})}}I_{j}}} \right)$

in which

I₁, I_(j), . . . I_(n) represents samplings of the drawn currentintensity.

According to another aspect of the invention, there is provided a systemto regulate the speed of a motor supplied from a source of alternatingvoltage via controlled switch means to apply to this motor a voltage ofvariable waveform, for practicing the process according to theinvention, this system comprising:

means to predetermine the periodic instants of triggering saidcontrolled switch means,

means to supply control signals for triggering said controlled switchmeans, and

means to measure the current drawn by the motor.

According to the invention, this system comprises moreover control andprocessing means arranged to:

compute a quantity of surface corresponding to the current drawn in atime window defined between an instant of establishing the current and afollowing instant of extinguishing this current;

computing a duration of the next time of blocking the controlled switchmeans, and

controlling the triggering of said switch means at the end of thisblockage time.

Other particularities and advantages of the invention will becomeapparent from the following description. In the accompanying drawings,given by way of non-limiting example:

FIG. 1 is a synoptic diagram of a first example of embodiment of asystem of speed regulation according to the invention;

FIG. 2 is a synoptic diagram of a second embodiment of a system forspeed regulation according to the invention; and

FIG. 3 is a chronogram including several characteristic waveformsobserved with the process of regulation according to the invention.

There will now be described two examples of embodiment of a system ofregulation according to the invention, with reference to FIGS. 1 and 2.

A system of regulation 1 according to the invention is adapted toregulate the speed of a motor M, for example a universal motor, suppliedwith variable voltage from a monophase alternating source (L, N) bymeans of triac 15. For measuring current, a double bridge rectifyingcircuit 19, constituted conventionally by four bridged diodes D1-D4, isdisposed in series with the triac 15 and the motor M, and resistance Ris connected at the output of this rectifying circuit. The voltage atthe terminals of this resistance gives an image of the current passingthrough the motor M.

The regulation system 1 is constructed about a microcontroller 10supplied by a supply and synchronization module 18 connected to thealternating source (L, N). The microcontroller 10 receives at its inputa signal from an initialization module controlled by the supplyingsynchronization module 18, and a signal from a safety module 16.

The regulation system 1 moreover comprises a module 11 for measuringcurrent receiving at its input the voltage across the terminals of theresistance R and sending to the microcontroller 10 an input signalrepresentative of the current drawn, an interface module 12 forcontrolling the triac 15 receiving a control signal emitted by themicrocontroller 10, a keyboard 13, and a display module 14. Themicrocontroller 10 includes an analog-digital conversion function, usedto generate internally a digital representation of the current drawn.

There could also be provided, referring to FIG. 2, in which thecomponents and modules common to FIG. 1 are given the same referencenumerals, another configuration for measuring the current drawn within asystem 2 for regulation of speed according to the invention. In thisother configuration, there is carried out with a single diode D a simplealternating rectification of the voltage at the terminals of theresistance R.

There will now be described an embodiment of the regulation processaccording to the invention, particularly with reference to FIG. 3. Thisprocess comprises first of all a computation sequence of the surfacequantity S_(I), which comprises the following steps:

taking a number n of samples of the intensity of current drawn by themotor, between an instant t_(i) at which the current is established, andan instant t_(f) of extinction of the current,

calculating surface elements,

summing the surface elements,

computing the surface quantity SI.

As to the current samplings, the sampling period t₁ is for exampleselected to be 50 μs. The samples are taken between instant t₁ ofestablishing the current and the instant t_(f) of extinction of thecurrent during a sampling period T_(I). The number n of samples takenduring this period can be determined by the relation:$n = {\frac{T_{I}}{t_{I}} + 1}$

The computation of the surface elements s₁, . . . , s_((n−1)) is carriedout in the following manner:$s_{1} = {t_{I}\quad \frac{\quad {I_{1} + I_{2}}}{2}}$$s_{({n - 1})} = {t_{I}\quad \frac{I_{({n - 1})} + I_{n}}{2}}$

There is then carried out the summation of all the surface elements thuscomputed: $S_{I_{1}} = {\sum\limits_{e = 1}^{e = {({n - 1})}}S_{e}}$

or again$S_{I_{1}} = {t_{I}\left( {\frac{I_{1} + I_{n}}{2} + {\sum\limits_{j = 2}^{j = {({n - 1})}}I_{j}}} \right)}$

The precision of measurement of surface depends on the value of thesampling period t_(I). This precision is higher the shorter the samplingperiod. Moreover, this sampling period is in practice selected to beconstant, which permits processing a surface quantity S_(I) that nolonger refers to the parameter t_(I).

The surface quantity S_(I) can then be expressed in the followingmanner:$S_{I} = \left( {\frac{I_{1} + I_{n}}{2} + {\sum\limits_{j = 2}^{j = {({n - 1})}}I_{j}}} \right)$

There will now be described a manner of computing the time of delay tofiring of the triac 15. The startup of motor M is carried out in aprogressive manner until the surface quantity reaches a minimum valueS_(Imin). Beyond this value, the process of regulation according to theinvention enters into action by carrying out the following operations:

a) a computation of the surface quantity SI for each period of thesector or each half alternation;

b) a computation of the preliminary duration of the next blocking timeof the triac (t′) by applying the following relation:$t^{\prime} = {\frac{T_{v}}{2} - {k_{v} \cdot P_{I}}}$

wherein k_(v) is a proportionality factor connected to the type of motorand to the desired speed, and

P_(I) is a parameter representative of the surface quantity S_(I),

and in the case of a progressive variation of the time of blocking,

c) a computation of a coefficient C of energetic correction, and

d) the computation of the blocking time effectively applied to thetriac.

The parameter P_(I) corresponds to S_(I), in the regime of operation inwhich linearity between the parameters t′ and the quantity of surfaceS_(I) is verified. In the contrary case, the parameter P_(I) is used asan indicator of a memory zone containing the blockage time t′.

In a linear regime, the blockage time t′ can be determined by thefollowing relation:$t^{\prime} = {\frac{T_{v}}{2} - {k_{v}\left( {\frac{I_{1} + I_{n}}{2} + {\sum\limits_{j = 2}^{j = {({n - 1})}}I_{j}}} \right)}}$

In practice, so as to avoid any pumping phenomenon of the motor, thecorrection of the firing time of the triac is carried out in thefollowing manner:

by successive approaches in the direction of increasing time ofconduction of the triac;

abruptly in the direction of decrease of the conduction time of thetriac.

Thus, if the motor needs to be undersupplied, the new starting time canbe applied directly without particular precaution. The inertia of themotor generally dampens possible speed variations.

On the contrary, if the motor needs supplemental energy, the new firingtime of the triac is introduced in a progressive manner. To do that, thesystem computes a predetermined fraction f, for example one-eighth, ofthe difference between the last time t⁻ of blocking the triac and thenew computed blocking time t′. The difference between the last appliedblocking time t⁻ and the fraction thus computed, gives the nextprovisional time t⁺ for blocking of the triac. There is thus obtainedfor the provisional blocking time t⁺the following relation:

t ⁺ =t ⁻ +f(t′−t ⁻)

t ⁺ =t ⁻(l−f)+(f·t′)

or again,$t^{+} = {{t^{-}\left( {1 - f} \right)} + {f\left( {\frac{T_{v}}{2} - {k_{v}\left( {\frac{I_{1} + I_{n}}{2} + {\sum\limits_{j = 2}^{j = {({n - 1})}}I_{j}}} \right)}} \right)}}$

The computation of the energy correction coefficient C is carried out byapplying the following relation:$C = {2\left( {{1\text{,}5} - {\sin \left( {2 \cdot \pi \cdot \frac{t^{+}}{T_{V}}} \right)}} \right)}$

The use of this energy correction coefficient permits giving the motorenergy proportional to the time of conduction of the triac,independently of the position of this latter on the sinusoidal curve.

The final time t_(c) of blockage of the triac is thus:$t_{c} = {{\left( \frac{C - f}{C} \right)\quad t^{-}} + {\frac{f}{C}\left( {\frac{T_{v}}{2} - {k_{v}\left( {\frac{I_{1} + I_{n}}{2} + {\sum\limits_{j = 2}^{j = {({n - 1})}}I_{j}}} \right)}} \right)}}$

The complete expression of this blockage time t_(c), as a function ofthe samplings of current intensity and of the preceding blockage timet⁻, is given below:$t_{c} = {\left( {2\left( {{1\text{,}5} - {\sin \quad {2 \cdot \pi \cdot \left( T_{v} \right)^{- 1}}\left( {{t^{-}\left( {1 - f} \right)} + {f\left( {\frac{T_{v}}{2} - {k_{v}\left\lbrack {\frac{I_{1} + I_{n}}{2} + {\sum\limits_{j = 2}^{j = {({n - 1})}}I_{j}}} \right\rbrack}} \right)}} \right)}} \right)} \right)^{({- 1})}\quad \times \left( {{\left( {\left( {2\left( {{1\text{,}5} - {\sin \quad {2 \cdot \pi \cdot \left( T_{v} \right)^{- 1}}\left( {{t^{-}\left( {1 - f} \right)} + {f\left( {\frac{T_{v}}{2} - {k_{v}\left\lbrack {\frac{I_{1} + I_{n}}{2} + {\sum\limits_{j = 2}^{j = {({n - 1})}}I_{j}}} \right\rbrack}} \right)}} \right)}} \right)} \right) - f} \right)t^{-}} + {f\left( {\frac{T_{v}}{2} - {k_{v}\left\lbrack {\frac{I_{1} + I_{n}}{2} + {\sum\limits_{j = 2}^{j = {({n - 1})}}I_{j}}} \right\rbrack}} \right)}} \right)}$

This computation can be implemented without difficulty in an eight-bitmicroprocessor such as microprocessor 8051 of the Intel company.

It is to be noted that the steps of the process which have beendescribed are repeated in cyclic fashion, at each alternation or halfalternation of the supply voltage. The computing time required by themicroprocessor to execute these steps is practically negligible beforethe wave period of supply voltage. An analog-digital conversion of eightbits of the measurements of current drawn is in principle sufficient toobtain a correct regulation of a motor.

Of course, the invention is not limited to the examples which have beendescribed, and numerous arrangements can be made of these exampleswithout departing from the scope of the invention. Thus, the processaccording to the invention can be used in supply and regulation systemsthat are more complex than that which has been described. Moreover,there can be provided other manners of energy correction and progressivevariation of the blocking and conduction times.

What is claimed is:
 1. Process to vary and regulate the speed of a motor (M) supplied from an alternating voltage source (L, N) via controlled switch means (15) to apply to this motor (M) a voltage (v(M)) of variable waveform, comprising regulation of the periodic instance of triggering said controlled switch means (15), characterized in that it moreover comprises, at least once per period of the alternating voltage, the following steps: a surface quantity (S_(I)) is computed corresponding to the current drawn (I(M)) in a time window (FT) defined between an instant (t_(i)) of establishing the current and a following instant (t_(f)) of extinction of this current; a duration of the next time (t′) of blocking said controlled switch means (15) is computed, and the triggering of said switch means (15) is controlled at the end of this blockage time (t′).
 2. Process according to claim 1, characterized in that for the computation of the surface quantity (S_(I)), there are taken a plurality of samplings (I₁ . . . I_(j) . . . I_(n)) of the current intensity (I(M)) drawn by the motor (M), in a time window (FT) comprised between an instant (t_(i)) of establishment of the current and an instant (t_(f)) of extinction of this current; the surface elements (s₁, . . . , s_(n−1)) are computed from the taken samples, the surface elements (s₁, . . . , s_(n−1)) are summed to determine a surface quantity (S_(I)) corresponding to the current drawn (I(M)) by the motor (M) during a conductive phase of the controlled switch means (15).
 3. Process according to claim 1, characterized in that a preliminary duration t′ of the next blocking time of the controlled switch means (15) is computed by using the following relation: $t^{\prime} = {\frac{T_{v}}{2} - {k_{v} \cdot P_{I}}}$

in which T_(v) is the period of the alternating supply voltage, k_(v) is a proportionality factor connected to the type of motor and to the desired speed, and P_(I) is a parameter associated with the computed surface quantity.
 4. Process according to claim 3, characterized in that the parameter (P_(I)) is used as the indicator of a memory zone containing blockage time values t′ corresponding to the values of the surface quantity (S_(I)).
 5. Process according to claim 3, corresponding to regimes of operations in which the linearity between the respective parameters of blockage time (t′) and surface quantity (S_(I)) is substantially verified, characterized in that the parameter (P_(I)) is substantially equal to the surface quantity (S_(I)).
 6. Process according to claim 3, characterized in that, for transitional regimes in which the motor requires an energy supplement, it comprises moreover a correction of the duration of each next blockage time (t′), this correction corresponding to a difference between the next blockage time (t⁺) and the last applied blockage time (t⁻) which is limited to a predetermined fraction (f) of the difference between the new computed blockage time (t′) and the last applied blockage time (t⁻).
 7. Process according to claim 6, characterized in that it moreover comprises a computation of the coefficient of energy correction (C) by using the relation: $C = {2\left( {{1\text{,}5} - {\sin \left( {2 \cdot \pi \cdot \frac{t^{+}}{T_{V}}} \right)}} \right)}$

and in that the predetermined fraction (f) is divided by this energy correction coefficient (C).
 8. Process according to claim 3, characterized in that, for transitional regimes corresponding to a decrease of the conductive time of the controlled switch means (15), there is directly applied the new computed blockage time (t′).
 9. Process according to any claim 2, characterized in that the surface quantity (S_(I)) is computed by using the following relation: $S_{I} = \left( {\frac{I_{1} + I_{n}}{2} + {\sum\limits_{j = 2}^{j = {({n - 1})}}I_{j}}} \right)$

in which I_(l), I_(j), . . . I_(n) represent samplings of the intensity of the drawn current.
 10. System (1, 2) to regulate speed of a motor (M) supplied from a source of alternating voltage (L, N) via controlled switch means (15) to apply to this motor (M) a voltage of variable waveform, this system comprising: means to predetermine the periodic instants of triggering said controlled switch means, means to supply triggering control signals to said controlled switch means, and means (R, 11, 19) to measure the current (I(M)) drawn by the motor (M), characterized in that it moreover comprises control and processing means (10) arranged to: compute a surface quantity (S_(I)) corresponding to the current drawn during a time window (FT) defined between the instant (t_(i)) of establishment of the current and a following instant (t_(f)) of extension of this current; compute a next blockage time duration (t′, t_(c)) for the controlled switch means (15), and ordering a triggering of said switch means (15) at the end of this blockage time (t′, t_(c)). 